Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $142.47   10.410%   $157.3011   $157.30   $157.30   $157.30  
  Purchase #2 $250.44   5.616%   $264.5047   $264.50   $264.50   $264.50  
  Purchase #3 $33.43   4.602%   $34.9684   $34.97   $34.95   $35.00  
  Purchase #4 $177.90   7.337%   $190.9525   $190.95   $190.95   $191.00  
  Purchase #5 $129.34   8.551%   $140.3999   $140.40   $140.40   $140.40  
  Purchase #6 $217.98   7.363%   $234.0299   $234.03   $234.05   $234.00  
  Purchase #7 $104.87   3.210%   $108.2363   $108.24   $108.25   $108.20  
  7 purchase totals = $1,056.43       $1,130.3928   $1,130.39   $1,130.40   $1,130.40